1. Field of Invention
The present invention relates to a battery.
2. Description of Related Art
In recent years, with a background of increasing environmental protection activities, introduction of electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV) has been demanded. Secondary batteries for feeding electrical power to driving motors of such vehicles are required to have high-energy density which is unachievable with a single battery. The batteries in practical use for these applications are usually a plurality of unit cells connected in series and/or in parallel.
However, these batteries have a problem in that, if one of the unit cells connected in series and/or in parallel fails or becomes defective, the entire battery is no longer be unusable.
Countermeasures have been taken to avoid this situation, improving connection arrangement between unit cells.
Japanese Patent Application Laid-Open Publication No. H8(1996)-241705 discloses a battery which consists of series-connected groups of parallel-connected unit cells. In this battery, each unit cell is connected to at least one unit cell in parallel. Therefore, even when one of the unit cells fails or becomes defective, charge/discharge can still be carried out in the other unit cell connected thereto in parallel. Hence, the entire battery remains usable.